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October 18, 2007

Our First Lunar Program: What did we get From Apollo?

by Sam Savage

American plans now call for a return of humans to the Moon by around 2020. What can we hope to gain from such a program? It will be helpful to look back at our first lunar program, Apollo, and ask what we got from it, beside some 850 pounds of rock and soil "“ fascinating to geologists, but perhaps not to all taxpayers. I will try to summarize highlights of the payoff from Apollo.

What was the "Apollo Program"? There was much more to it than Neil Armstrong's "one small step," and even more than the following five lunar landings "“ any one of which would have been a gigantic accomplishment. First, Apollo began with the Gemini Program, which was solely a technological warm-up for Apollo. Gemini was the first true American spaceship, with propulsion, radar, on-board computers, and extravehicular activity ("space walk") capability. Ten manned Gemini missions were flown, developing the technological and operational capability needed for the following lunar program. However, the Gemini astronauts carried out many scientific experiments, in addition to practicing various space-flight techniques such as orbital rendezvous.

The Apollo lunar missions are now in the history books. However, there were two Earth-orbital ones, Apollo 7 and 9, that carried out experiments such as multispectral terrain photography. This uses combinations of different types of light, such as infrared and ultraviolet, that reveal things not seen using only visible light, like diseased trees or crops. This photography was a feasibility test for Landsat (launched in 1972). But there was much more to the Apollo Program. First, the Apollo hardware was used for America's first space station, Skylab, in 1972 to 1973. The Skylab astronauts carried out dozens of scientific experiments, such as orbital sea-surface radar, and operated a solar observatory with extremely valuable results.

In 1975, the Apollo spacecraft flew for the last time, carrying out a rendezvous and docking with a Soviet Soyuz spacecraft. This cooperative effort was at least one bridge across the political divide of the Cold War. In summary, the Apollo Program, properly defined, was much broader than most people realize. Furthermore, it was not enormously expensive relative to the American federal budget of the day. The several sub-programs mentioned cost a total of about $30 billion by the end of Fiscal Year 1975. To allow for inflation, a same-year comparison may help: the FY 75 NASA budget was $3.3 billion, and the FY 75 Food Stamp Program $5.5 billion.

What did we get for this $30 billion? The term "spinoff" is often used, but this tends to trivialize the Apollo results. However, here are some of the eventual results of the Apollo Program.

First, and perhaps most important: it was realized at the time of President Kennedy's 1961 proposal that the primary motivation for sending a man to the Moon was political, not scientific. The Soviet Union at the time had a commanding lead in space flight, and was a belligerent and expansive power in the Cold War. Did Apollo end the Cold War? Of course it didn't. But no less than Nobel laureate Andrei Sakharov and two colleagues issued an open letter to the Soviet government in 1970, calling for democratization of the USSR, specifically citing the American Moon landing as evidence of the superiority of democracy. The Soviet Union did have a lunar program intended to put a man on the Moon, but as the world saw, the United States won the race.

Even if the Apollo missions had never landed on the Moon, the program as a whole stimulated projects that learned an enormous amount about our own planet, Earth. The earliest and even now one of the most productive of these projects was Landsat, agreed by even the most severe NASA critics to have been an enormously valuable program. But how can Landsat be considered a result of Apollo?

The answer goes back to the Gemini Program, whose astronauts took hundreds of high-resolution color photos of the Earth with 70mm cameras as part of terrain and weather photographic experiments. Even in 1965, weather satellite pictures were familiar, but the Gemini photos were stunningly better. Published widely, in magazines such as the National Geographic (circulation in 1966 some 6 million), they triggered interest in space photography of the Earth's surface, as distinguished from its atmosphere.

To summarize a long and complex story: As stated by the then-director of the U.S. Geological Survey, Bill Pecora, the value of the Gemini and Mercury photos stimulated the Interior Department to propose an Earth resources observation satellite program, EROS, in 1966. After interagency negotiation, this proposed satellite became ERTS, the Earth Resources Technology Satellite, managed by Goddard Space Flight Center, and shortly re-named Landsat. So Landsat really was an outgrowth of the Apollo Program, as testified to by the head of another agency, not NASA.

The Manned Spacecraft Center, now Johnson Space Center, was built for the Apollo Program. It was realized that much orbital reconnaissance of the Moon would be necessary for the Apollo landings. Accordingly, JSC began a broad program of remote sensing, using airborne cameras and other instruments, in preparation for the Moon. This program soon triggered enormous progress in remote sensing in general, and combined with the Gemini photography led to Landsat and soon after its foreign counterparts such as France's SPOT (Systeme pour l'Observation de la Terre). Needless to say, the JSC remote sensing efforts were soon applied successfully to the Moon, but they also stimulated orbital survey techniques of the Earth as well, techniques that have long since expanded to many American and international programs. But this revolution in remote sensing owes much to the Apollo Program.

As mentioned above, Skylab was part of the Apollo Program, and carried out many remote sensing observations analogous to those of Landsat. However, one which was not analogous was sea-surface radar altimetry. Skylab carried a radar aimed down at the Earth, including the oceans. Microwaves do not penetrate electrical conductors, such as metals or water, and the radar return over oceans was from the sea surface. It was found that the Skylab radar over depressions in the ocean floor, such as the Puerto Rico trench, actually showed a subdued replica of such depressions in the overlying sea surface. Over seamounts "“ underwater volcanoes "“ the sea surface forms a slight mound. "Slight" is a relative term "“ the sea surface depression over the Puerto Rico trench is more than 20 meters (yards) deep.

The explanation for this surprising discovery is that the excess mass of, for example, a seamount, pulls the surrounding ocean horizontally towards it, thus producing a slight bulge in the overlying sea surface. The opposite effect occurs over a trench, which is a mass deficiency. The Skylab radar results triggered long-term and continuing sea surface radar surveys, which have made possible detailed global maps of the sea floor impossible by any other method. So Apollo, properly defined, helped explore the part of our own planet hidden by the oceans.